Variability of East African rainfall based on multiyear RegCM3 simulations

摘要

The International Center for Theoretical Physics (ICTP) regional climate model version 3 (ICTP-RegCM3) multiyear simulations of East Africa rainfall during the October-December, short rains season are evaluated. Two parallel runs; based on NCEP reanalysis and NASA FvGCM lateral boundary conditions are performed. The simulated monthly and seasonal rainfall climatology as well as the interannual variability are found to be fairly consistent with the observations. The model climatology over specific homogeneous climate subregions, except central Kenya (CKE) highlands, also reasonably agrees with the observed. The latitude-time evolution (intraseasonal variability) of the simulated seasonal rainfall exhibits two distinct modes of behavior. The first is a quasistationary mode associated with high rainfall throughout the season within the equatorial belt between 1 degrees S and 2 degrees N. The second mode is associated with the intertropical convergence zone (ITCZ)-driven southward migration of regions of rainfall maxima as the season progresses, which is also consistent with the observed. Furthermore, observed rainfall variability over distinct homogeneous climate subregions is also fairly reproduced by the model, except over central Kenya highlands and northeastern parts of Kenya. The spatial correlation between the simulated seasonal rainfall and some of the global teleconnections (DMI and Nino3.4 indices) shows that the regional model conserves some of the observed regional 'hot spots' where rainfall-ENSO/DMI associations are strong. At the same time, unlike observations, the model reveals that along the East Africa Rift Valley and over western parts of the Lake Victoria Basin, the association is weak, perhaps an indication that nonlinear interactions between local forcing (captured by the model) and large-scale systems either suppress or obscur the dominant influence of the teleconnections on rainfall over certain parts. Copyright (C) 2006 Royal Meteorological Society.